Electron-Beam-Probing Studies of Beam—Plasma Interactions

This paper describes experimental observations of electron-beam—plasma amplification in a low-pressure, beam-produced, mercury-vapor discharge. A nonperturbing probing technique, employing a fine auxiliary electron beam, was used to measure rf growth, phase velocity, and axial and radial electric-field profiles in the interaction region. The comprehensive data obtained have been compared with predictions based on cold- and warm-plasma theories of beam—plasma amplification. It is concluded that the experimental growth rates and electric-field profiles are approached more closely by warm-plasma theory, but that the measured phase velocities are somewhat slower than either theory suggests. The electric-field profiles are smoother than expected, probably owing to the beam boundary being less sharp in practice than is assumed in the theories.